设计模式之状态模式

将当前工作场景所要做的工作内容（工作内容互相之间有顺序切换关系）交给具体状态类处理（每一种状态处理特定行为），避免所有繁琐的业务包杂在工作场景进行过多的分支切换操作，经过这样的分层之后，使得状态的切换也只是在状态类之间切换（通过传递工作场景对象指针或引用），虽说代码量增加了不少，但是对于业务的处理清晰了许多。

例一：

state.h

#ifndef STATE_H#define STATE_H#include <iostream>using namespace std;class Context;//抽象状态类class State{public:    //抽象状态的纯虚函数，子类需继承实现具体行为，依赖Context指针做为状态切换参数    virtual void Handle(Context* pContext) = 0;};//工作场景class Context{public:    //定义_state的初始状态    Context(State* pState)    {        _state = pState;    }    ~Context();    //对请求做处理，并设置下一状态    void Request()    {        if(NULL != _state)        {            _state->Handle(this);        }    }    void ChangeState(State* pState)    {        _state = pState;    }private:    State* _state;};//具体状态类Cclass ConcreteStateC : public State{public:    //执行该状态的行为并改变状态    virtual void Handle(Context* pContext);};//具体状态类Bclass ConcreteStateB : public State{public:    //执行该状态的行为并改变状态为C状态    virtual void Handle(Context* pContext)    {        cout << "ConcreteStateB" << endl;        pContext->ChangeState(new ConcreteStateC());    }};//具体状态类Aclass ConcreteStateA : public State{public:    //执行该状态的行为并改变状态为B状态    virtual void Handle(Context* pContext)    {        cout << "ConcreteStateA" << endl;        pContext->ChangeState(new ConcreteStateB());    }};#endif // STATE_H

state.cpp

#include "state.h"//执行该状态的行为并改变状态为A状态void ConcreteStateC::Handle(Context *pContext){    cout << "ConcreteStateC" << endl;    pContext->ChangeState(new ConcreteStateA());}

main.cpp

int main(){    State* pState = new ConcreteStateA();    Context* pContext = new Context(pState);    pContext->Request();    pContext->Request();    pContext->Request();    pContext->Request();    return 0; }

例二：
car.h

#ifndef _CAR_H_#define _CAR_H_class Car;class State{    public:        virtual void forward(Car *) = 0;        virtual void turnLeft(Car *) = 0;        virtual void turnRight(Car *) = 0;        virtual void display() = 0;};class Car{    public:        Car(){}        Car(int i,int j):x(i),y(j)        {            state = new North();        }        ~Car()        {            delete state;        }        int getX(){ return x;   }        int getY(){ return y;   }        void forward();        void turnLeft();        void turnRight();        void disp();        class North : public State        {            void forward(Car *);            void turnLeft(Car *);            void turnRight(Car *);            void display();        };        class South : public State        {            void forward(Car *);            void turnLeft(Car *);            void turnRight(Car *);            void display();        };        class East : public State        {            void forward(Car *);            void turnLeft(Car *);            void turnRight(Car *);            void display();        };        class West : public State        {            void forward(Car *);            void turnLeft(Car *);            void turnRight(Car *);            void display();        };    private:        int x;        int y;        State *state;};#endif

car.cpp

#include <iostream>#include "car.h"using namespace std;void Car::forward(){    /*    switch(state)    {        case 0:            x++;break;        case 1:            x--;break;        case 2:            y--;break;        case 3:            y++;break;        default:            break;    }*/    state->forward(this);}void Car::turnLeft(){    //State *p = state;    state->turnLeft(this);    //delete p;}void Car::turnRight(){    //State *p = state;    state->turnRight(this);    //delete p;}void Car::disp(){    cout << "state: ";    state->display();    cout << getX() << " , " << getY() << endl;}//northvoid Car::North::forward(Car *c){    c->y++;}void Car::North::turnLeft(Car *c){    c->state = new West();}void Car::North::turnRight(Car *c){    c->state = new East();}void Car::North::display(){    cout << "North:";}//southvoid Car::South::forward(Car *c){    c->y--;}void Car::South::turnLeft(Car *c){    c->state = new East();}void Car::South::turnRight(Car *c){    c->state = new West();}void Car::South::display(){    cout << "South: ";}//eastvoid Car::East::forward(Car *c){    c->x++;}void Car::East::turnLeft(Car *c){    c->state = new North();}void Car::East::turnRight(Car *c){    c->state = new South();}void Car::East::display(){    cout << "East:";}//westvoid Car::West::forward(Car *c){    c->x--;}void Car::West::turnLeft(Car *c){    c->state = new South();}void Car::West::turnRight(Car *c){    c->state = new North();}void Car::West::display(){    cout << "West: ";}

main.cpp

#include <iostream>#include "car.h"using namespace std;int main(){    Car c(0,0); // 0,0    c.forward();//0,1    c.forward();//0,2    c.forward();//0.3    c.disp();    c.turnRight();    c.disp();    c.forward();//1,3    c.forward();//2,3    c.forward();//3,3    c.disp();    return 0;}